Short-term temporal variations in iron concentration and speciation in a canal during a summer algal bloom

Abstract

We conducted field investigations in a canal connected to Lake Kasumigaura (Japan) twice weekly during a summer algal bloom to understand the temporal variations in dissolved iron and its speciation, and the controlling factors. Dissolved iron (DFe), which is operationally defined as that passing through a 0.2-mm pore filter, acid-labile particulate iron (LP-Fe), and chemical speciation of dissolved iron were analyzed. LP-Fe was extracted from the suspended solids (SS) on 0.2-mm pore-size filters after a 2 h soak in 25 % (4.5 M) acetic acid. The chemical speciation of dissolved iron was determined using cathodic stripping voltammetry. The concentration of D-Fe ranged from 72 to 1354 nM and that of filterable labile iron (FL-Fe) from 5 to 881 nM, and both increased markedly after two heavy rains. The increased D-Fe and FL-Fe appeared to be removed within a few days. The concentrations of LP-Fe ranged from 4.1 to 16.1 mM, were much higher than those of D-Fe, and did not increase after the rains. There was a significant correlation (jrj = 0.88, P < 0.01) between ln[D-Fe] and pH. This suggests that the dynamics of D-Fe in the canal depend upon the cycle of adsorptive removal onto the surface of SS at high pH and desorptive supply from the surface of SS at low pH. Moreover, D-Fe concentration would also be controlled by the formation of iron oxyhydroxides amorphous particles at high pH and dissolution at low pH. The percentage of organically complexed iron ranged from 35 % to 99 % and varied markedly at time scales of days to weeks. There was a significant correlation (jrj = 0.60, P < 0.01) between the percentage of organically complexed iron and the log of the cell density of Microcystis spp.. This suggests that the growth of specific algal species affects iron speciation in the canal.

Effects of iron deficiency on the growth and photosynthesis of three bloom‐forming cyanobacterial species isolated from Lake Taihu

“…North et al () have indicated that phytoplankton communities in the eastern basin of Lake Erie experienced co‐limitation by P, N, and Fe during the summer period of thermal stratification and suggested that this condition might be more widespread in large areas of the Laurentian Great Lakes. Nagai et al () have also found a significant correlation between the percentage of organically complexed iron and Microcystis spp. cell density during a summer microalgal bloom, suggesting that iron availability could influence the formation of Microcystis spp.…”

Voltammetric methods for speciation analysis of trace metals in natural waters

“…The speciation of Fe has been investigated in different natural water samples. Nagai et al (2008) extensively investigated the speciation of Fe in river water using the CLE-AdCSV method with NN as the AL [131]. Results showed that Fe concentration and speciation (organic Fe) were controlled by pH and algal growth, respectively, with the established quantitative model successfully used for the prediction of organically bound Fe concentration based on pH and algal cell density data.…”